People go looking for their underground water pipe for three reasons: the water meter says there is a leak, they are about to dig for a driveway, extension or garden wall and do not want to hit it, or they need to replace an old lead pipe and want to know how much of the garden is involved. In every case the problem is the same. The pipe is buried, it is private, and there is almost never a drawing of it.
This guide explains where the supply pipe normally runs, the checks that narrow it down for free, and the locating methods professionals use, including why the right one depends on what the pipe is made of.
Which water pipe is yours?
The water company's main runs under the road. A short communication pipe branches off it to your boundary, usually ending at an external stop tap or meter under a small cover in the pavement or just inside your front boundary. From that point to the house the pipe is the supply pipe, and it belongs to the property owner. It is the owner's responsibility to maintain and repair, and it is the section you are trying to find.
In older London terraces one supply pipe sometimes feeds several houses before branching, which changes both the route and who is responsible for it. Our guide to shared supply pipes covers how to tell.
Start with the two ends
You cannot trace a line without both of its ends, and both can usually be found without equipment.
The outside end. Look along the pavement and front boundary for a small square or round cover, often marked with a W or the water company's name. Lift it and you should find a stop tap, a meter or both. On a shared frontage there may be several, and running a tap inside while watching which meter dial moves tells you which one is yours.
The inside end. The internal stopcock is where the supply pipe comes up through the floor. In London houses it is most often under the kitchen sink, but it also turns up under the stairs, in a front room under a floorboard, in a downstairs toilet or in the cellar. Where it rises tells you which wall the pipe comes through.
Once you have both, mark them on a sketch of the front of the property. The pipe normally runs between them by the shortest practical route, but not always: installers went round old trees, steps, bay windows, cellars and coal holes, and extensions or new paths may have been built over a pipe that was laid decades earlier.
How deep is a water supply pipe?
For new pipes the guidance under the Water Supply (Water Fittings) Regulations 1999 is a depth of at least 750mm and no more than 1350mm below finished ground level, deep enough to protect the pipe from frost and surface damage. Water companies publish the same figures in their guidance for anyone laying a new supply.
Older pipes were often laid shallower, and landscaping changes the depth after the event: a raised patio adds cover, a lowered driveway takes it away. Treat 750mm as what a modern pipe should be at, not a promise about yours, and dig by hand near the likely route.
What is the pipe made of?
This decides which locating method will work, so it is worth checking at the stopcock where the pipe comes out of the floor.
| Material | How to recognise it | Can a pipe locator follow it? |
|---|---|---|
| Blue MDPE plastic | Blue plastic, the modern standard | Not directly. It needs a sonde pushed inside, or acoustic or tracer gas methods. |
| Black polythene | Black plastic, found on older plastic supplies | Not directly, same as blue. |
| Lead | Dull grey, soft, scratches to a shiny silver, with rounded wiped joints | Yes, it conducts a signal. |
| Copper | Orange-brown metal | Yes. |
| Galvanised iron | Grey steel with threaded joints | Yes. |
A pipe that comes up through the floor in copper may still be plastic or lead underground, because the last section indoors is often replaced on its own. If you are not sure, a professional will usually establish the material at both ends before choosing the method.
Can a water company map show where my pipe is?
Only part of it. Water companies keep records of their mains and, in many cases, their communication pipes, and these can be obtained through their asset location or property search services. They do not usually record private supply pipes, because those were laid by or for the owner. So a map will tell you where the main is in the road and roughly where your connection leaves it, which is useful, but not where the pipe crosses your garden.
Deeds and old building control drawings occasionally show a route. It is worth a look before paying anyone, but most older London properties have nothing on file.
How do professionals locate a buried water pipe?
Signal locating on metal pipe. A signal generator is connected to the pipe at the stop tap or stopcock, and a receiver walked over the ground picks the signal up along the line of the pipe, with an estimate of depth. It is fast and accurate on copper, lead and iron.
A sonde on plastic pipe. Plastic carries no signal, so a small transmitter on a flexible rod is pushed into the pipe and followed from above. It needs the water off and access into the pipe at one end.
Acoustic listening. With water flowing, or with a leak present, ground microphones pick up the sound travelling along the pipe. It works on any material, and on a leaking pipe it finds the leak and the route together. Our guide to acoustic leak detection explains how.
Tracer gas. The pipe is drained and filled with a safe hydrogen and nitrogen mix, which rises through soil and paving where the pipe leaks and is picked up at the surface. It is the method for a plastic pipe that is leaking but too quiet to hear. See how tracer gas works.
Ground penetrating radar. Radar can show buried objects of any material, but on a small domestic pipe in mixed London ground its results need interpreting and it is rarely the first choice.
Divining rods and bent coat hangers come up a lot in searches. There is no mechanism by which they detect a pipe, and nobody should dig on the strength of them.
What if the reason you are looking is a leak?
Then do the meter test before anything else. Turn off the internal stopcock, make sure nothing is using water, and read the meter at the boundary twice, fifteen minutes apart. If it moves with the house isolated, water is escaping on the buried supply pipe between the meter and the house. Our guide to underground supply pipe leaks covers the test in detail, and leaks under a driveway covers the case where the route runs under paving.
Finding the route and the leak are usually one visit, and the aim is a single small excavation over the fault rather than a trench along the whole garden. Leak Detect London locates underground supply pipes and their leaks across London, with underground and water mains surveys at £300 to £500, the figure agreed before we start. Call 020 3912 0200 and tell us where your stop taps are.
Frequently asked questions
How do I find my water pipe underground without digging?
Find the external stop tap or meter and the internal stopcock first, since the pipe runs between them. To follow the route itself, a signal locator works on copper, lead and iron pipe, while plastic pipe needs a sonde inside it, acoustic listening or tracer gas.
How deep is a water pipe buried in the UK?
New supply pipes should be at least 750mm and no more than 1350mm below finished ground level under the Water Supply (Water Fittings) Regulations 1999 guidance. Older pipes are often shallower, and changes to the ground above since they were laid alter the depth.
Does the water company have a map of my supply pipe?
Usually not. Water company records cover their own mains and connections, not the private supply pipe from your boundary to the house. They will show where the main runs and roughly where your connection leaves it.
Can a metal detector find a water pipe?
A basic metal detector may pick up a shallow copper or lead pipe, but it gives no depth and misses deeper pipes. Plastic pipe cannot be detected by metal detectors at all.
Who is responsible for the water pipe under my garden?
The property owner. The supply pipe from the boundary stop tap to the house is private, so its upkeep and repair fall to the owner, even though it is outside and underground. Where one pipe serves several houses, responsibility is usually shared.
